Been playing this game for a while now and for the majority of my time playing, it has been enjoyable and there is definitely potential for this game. However, there is a list of suggestions which I think could make the experience much more exciting.

1.) Paywall issues. I understand people wanting to improve their team with cash and support the game for these transactions, but players shouldn't be made to pay to type 4 messages a day in global chat.
2.) Leagues. Leagues are good on all accounts, basic mode everyday to play. Ideally, I'd increase the rate of energy though. Another alternative would be if energy cap increased with club level.
3.) Friends. Energy gifting is a cool feature but achievements for Mutual assistance can be annoying since energy can only be claimed so many times a day. Being able to claim energy from each friend once a day would be awesome.
4.) Ranking matches are also generally good. Although, I'd like to see the skill boost rewards refresh as often as the Fame/Association stores.
5.) Stubs. 84 rated players require 20 stubs, whilst 85 rated players require 50 stubs for submission. The difference in prices leads to an approx 160-170% increase in fame costs for 16% additional value. 84's (Dzeko, Alli & Sane) sell for 840k compared to the 1million for 85 rated players like Carrasco.
6.) New Championship Update. Used to be a good mode to spend tokens on from ranking mode and allowed users to build up players or cash regardless of their level. However, with the new update, the AI trounces those who grind to high grades, and if they don't, you'll often face top 10 players, regardless of the quality of players in your team. It's fine to make the mode more competitive, but at least tone down the non user AI players because tournaments become impossible to win, it's genuinely easier to pull off wins against players in the top 20 than to beat an AI in cup grade 4. (This is the most important issue that HAS to be addressed because its almost unplayable for those who choose to grind).
7. Last but not least, the market. I'd suggest one of 3 options. The first is to remove selling fees. A 30% tax is taken off of all successful auctions, so why does the 2% fee on every list have to exist? Another alternative is to lower that 30% tax, even to 20-25%. I've seen a ronaldo on the market for 500million. Losing 150million on one sale is massive. Lastly, the option I'd most suggest is to increase the market slots (even if they increase slightly by level), being able to sell more than 10 items at a time would be massive even if selling fees increased incrementally like it does to enter additional tournaments/ranking matches etc. Even a 10-20 token cost to list more than 10 items would be welcomed at times.

I have to add to my point about the fame stores. 85+ players have a 200k fee to turn stubs into the player whereas 84's have a 50k fee. So the 160k difference in value between an 84 and 85 rated player minus the 30% market tax makes 112k difference after sale, when you have to pay 150k more to get the player and spend 2.5x the fame cost. Losing cash for spending 2.5x the fame has to be addressed, because its ludicrous.